Gate Keeper Security Alarm

IR based security alarm circuit can detect any movement and trigger the alarm. This circuit is very useful in homes, banks, shops, restricted areas where an alert alarm is needed on any movement. This circuit is based on IR sensor where an IR beam is continuously falling on a photodiode, and whenever this Infrared beam breaks, by any kind of movement, alarm is triggered.

IR sensor consist an IR LED and photodiode, in which IR LED emits IR radiation and photodiode detects the radiation. Photodiode conducts current in reverse direction, whenever light falls on it, and voltage across it changes, this voltage change is sensed by voltage comparator (like LM358) and generates output accordingly.

In this IR based security alarm circuit, we have placed IR LED in front of photodiode, so that IR light can directly falls on photodiode. Whenever someone moves through this beam, IR rays stops falling on photodiode and Buzzer start beeping. Buzzer automatically stops after some time, as buzzer is connected to 555 timer in monostable mode.

This kind of Alarm can also be build Laser light, (like Laser Security Alarm Circuit) but the benefit of using IR sensor is that IR light in invisible while Laser is visible. Although both are useful and have different scope.

Components

IR pair (IR LED and Photodiode)

555 timer IC

IC LM358

Resistor 100, 10k, 100k, 330, 220 ohm

Capacitor 10uF

Variable resistor – 10k

Buzzer

Circuit Diagram and Explanation

We have used op-amp LM358 in this circuit, LM358 has two voltage comparators inside it, and we have used one comparator here. Non-inverting end (PIN3) of voltage comparator is connected to the Photodiode and inverting end (PIN 2) of voltage comparator is connected to a variable resistor of 10k. Output of the voltage comparator (PIN1) is fed to the Trigger pin of 555 timer. 555 Timer is configured in monostable mode here.

While the IR radiation is falling on Photodiode, the voltage at the non-inverting end (+) of voltage comparator is higher than the inverting end (-) and the output of the comparator is HIGH. And as the comparator output is connected to the trigger PIN of the 555 timer, so the when the Trigger pin 2 is high, the 555 output is low. So during the period when the IR rays falls on Photodiode, the 555 timer output remains LOW. To understand the working of IR sensor with comparator LM358 go through this article: IR Sensor Module Circuit

Now when there is some movement, the falling of IR rays on Photodiode gets interrupted and the voltage at inverting end (Threshold voltage) of voltage comparator becomes higher than non-inverting end, for some moment. This makes the output of comparator LOW and also makes the Trigger PIN 2 of 555 timer LOW. This will trigger the 555 timer, and 555 timer’s OUTPUT goes HIGH and Buzzer beeps for short duration. Duration of the beep can be increased by changing the value of resistor R1 or capacitor C1 (RC network in monostable mode of 555 timer IC). Note that 555 IC gets triggered when Trigger PIN 2 gets LOW.

Notes:

Normally the range of IR LED is 2 meter, but it can be increased by using Lens.

AC alarm can be used in place of Buzzer, by using Relay.

IR LED and Photodiode must be properly aligned so that IR rays can directly falls on photodiode.

The sensitivity of the sensor can be changed by variable resistor RV1.

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We try our utmost best to provide our clients with unique and customize development & design. We create responsive design by HTML & CSS3. Our created web sites are of customize CMS which allows any user or admin to administrate it with comfort.

We are having feedback from our customers which inspire us to create android apps of multi leveled versions. Since clients’ positive responses we are trying to offer the best android apps to the market.

Since our inception of our company we try to give our best for the clients and for their satisfaction and clients also give us positive responses which inspire us to arrange new events for those who are interested in IT sectors.